ML20043G188
| ML20043G188 | |
| Person / Time | |
|---|---|
| Site: | Mcguire |
| Issue date: | 06/11/1990 |
| From: | Tucker H DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9006200010 | |
| Download: ML20043G188 (11) | |
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Charlotte, N C 28N2 (7b4)373 4531 DUKEPOWER June 11, 1990 U.S. Nuclear Regulatory Commission ATTNt Document Control Desk Washington, D. C.
20555
Subject:
McGuire Nuclear Station, Unit 2, Docket No. 50-370 Special Report Concerning Diesel Generator 2B Gentlemen:
Pursuant to Technical Specification (TS) 6.9.2 as specified by TS 4.8.1.1.3, find attached a special report concerning Diesel Generator 2B.
If there are any questions, please contact Steve LeRoy at 704-373-6233.
Very truly yours, 9 / h Y se-Hal B. Tucker Attachment SEL551 xc:
Mr. S.D. Ebneter, Administrator U. S. Nuclear Regulatory Commission, Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. D.S. Hood, Project Manager Office of Nuclear Reactor Regulation, USNRC Washington, D.C.
20555 Mr. P.K. Van Doorn Senior Resident Inspector, USNRC McGuire Nuclear Station 9006200010 900611 l
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U.S.-Nuclear Regulatory Commission
- ATTN: Document Control Desk June 11, 1990 Attachment No. 1 Duke Power Company McGuire Nuclear Station Diesel Generator 2B Special Report On May 10, 1990 at 1530, a Valid Failure occurred on Diesel Generator (DG) 2B.
Unit 2 was in Mode 1.
DG Start Attempt No. 793 was performed per the DG operability surveillance test (PT/2/A/4350/02B, weekly frequency).
The engine started; however, the +1mc for the generator voltage to reach 4160V was 11.3 seconds versus the Technical Specification requirement of 11
- seconds.
~This was the first Valid Failure in the last 20 Valid Tests and the eighth Valid Failure in the last 100 Valid Tests for DG 2B.
On a unit basis, this is the seventh Valid Failure in the last 100 Valid Tests of DG 2A and 2B combined (see Attachment No. 2 for additional narrative material required for the combined Seventh Valid Failure Report).
Surveillance testing remains on a weekly frequency.
Technical Specification Action Item Log entry no. 15476 was made and work request no. 14l124 was initiated to investigate the slow voltage time. The 50% set point on speed switches S1A1 and SIA2 was suspected because it controls field flash during the DG start. Also, the speed switches in general are a known reliability problem. A calibration was performed on both of the DG 2B speed switches. The 50% as found set points were found to be correct. The 95% and 97% set points were found to be incorrect.
Although the 50% set points were in tolerance, past history has indicated repeatability problems.
It is thought that an intermittent problem existed because of start time variances during recent starts.
.Recently removed Unit 1 speed switches were calibrated, checked for repeatability and installed on DG 2B.
Start Attempt No. 794 was successfully performed on May 11, 1990 at 1528. This run was a Valid Success. Generator voltage time to 4160V was 10.57 seconds which is normal.
. Action is already underway to improve speed switch reliability by replacing the current Airpax switches with a Dynalco SST-2400A switch that is thought to be more accurate and reliable. This Nuclear Station Modification (NSM),
MG-12316 has already been accomplished on the Unit 1 DGs and is scheduled to be implemented on the Unit 2 DGs during the September 1990 refueling outage.
1 1
U.S. Nuc1:cr R:guletory Commicsion ATTN: Document' Control Desk June 11, 1990 s
Attachment No. 2 Duke Power Company McGuire Nuclear Station Diesel Generator Special Report McGuire Technical Specification 4.8.1.1.3 requires that additional narrative material be provided (per USNRC Regulatory Guide 1.108 Revision 1, section C.3.b) if the number of failures in the last 100 Valid Tests (on a per nuclear unit basis) is greater than or equal to 7.
On May 10, 1990 a Valid Failure occurred on DG 2B, This was the seventh Valid Failure in the last 100 Valid Tests for the Unit 2 DGs.
Reliability Improvement Measures The following are descriptions and bases for corrective measures, taken or planned, to increase the reliability of the DGs.
On May.10, 1990 DG 2B failed to reach 4160V in the required 11 seconds due to an apparent slow actuation of the 50% set point on the DG speed switches.
This is thought to be an intermittent problem because of variation in recent start times.
a.
A modification will be performed on the Unit 2 DGs during the next outage (September 1990) to replace the speed switches with a more reliable switch. This modification is complete on Unit-1.
'l 10n October 27, 1989 DG 2B failed to start due to a failure of the 50%
contact on speed switch SIA2.
b.
Same corrective action as listed in item a above.
On October 5, 1989 DG 2B failed to start. The apparent failure was solenoid valve 2VGSV5172 not opening (though the failure mode discovered was a failure to close).
c.
The valve was replaced. Although the failure mode would not repeat on the test bench, no further problems of this nature have been noted.
d.
The control air line filter and solenoid valve were checked for r
foreign metal shavings such as the one found in the failed solenoid and no problem was found.
This is considered to be a random failure.
if U.S.-Nuclser Rtgulatory-Commission ATTN: Document Control Desk June 11, 1990 Attachment-No. 2 Page 2 On September 29, 1989 DG 2B failed to start due to either burned contacts on relay RVG1 or the 50% contact on a speed switch as discussed above. The root-cause was originally thought to be the burned contacts but after discovery of the speed switch failure (10/27/89) a caso can be made for that
.having also caused this failure.
Relay RVG1 was replaced on DG 2B.
It was later also replaced on c.
the other DGs.
f.
The circuit design was changed via station modification such that all four starting air solenoids are not energized through the same set of contacts. This change has been made on all DGs.
On August 29, 1989 DG 2B failed to reach 4160V in the required 11 seconds.
The root cause of the problem was a damaged speed sensor, g.
The machanical periodic maintenance tests (during outage) have been changed to remove the speed sensor prior to outage work and replace it before running the engine.
h.
New sensors were installed and the gap between the sensor and the gear videned.
i.
The speed sensors will be checked for damage every 9 months.
On July 27, 1989 DG 2B failed during a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> surveillance test (after 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br />) when 2 fuses in the voltage regulator feedback control circuit blow causing generator VARS to peg high. Operations personnel manually tripped the DG breaker. The root cause of the blown fuses is not certain but a contributing cause was the high room ambient temperature due to failure of a room ventilation recirculation damper.
j.
~A temporary modification was initiated to lock the recirculation damper closed. The damper was later repaired and the temporary modification cleared, k.
A control transformer and a circuit card in the voltage regulator were replaced as a preventative measure due to the high ambient temperature.
On July 26, 1989 DG 2B exceeded the 11 second 4160V requirement on the start. 'The cause of the failure could not be determined at the time of failure but'has since been determined to be the damaged speed sensor that also' caused the failure on August 29, 1989 (discussed previously). This failure was originally classified as an Invalid Test but has been changed to a Valid Failure upon further study. The speed sensor was likely damaged by maintenance activities during the outage; however, the damage scenario could not be agreed upon so this test is conservatively considered a Valid Failure.
1
U.S._Nuc1:ce R gulctory Commission ATTN Document Control Desk-l June 11, 1990 Attachment No. 2 Page 3 As a result of the numerous control related failures experienced since the last Unit 2 (EOC 5) outage, a continuing effort to evaluate the reliabili6y of our present design and initiato improvements is underway.
Personnel from the Maintenance Engineering Services section are working with the DG System Engineer, Design Engineering, and the site Projects section to get needed changes made. Some of the results so far include a new, more reliable speed switch. A more reliable governor to be installed during the September Unit 2 refueling outage should improve load stability during testing.
Modifications are scheduled to provide full flow lube oil filtration to the main bearings, main bearing temperature sensors, and starting air system improvements.
Other areas being reviewed are 1.
Pending station modification requests.
2.
Completed DG Reliability Centered Maintenance Study.
3.
Complete control system upgrade.
4.
PMs/ pts / Maintenance procedures.
5.
Instrumentation adequacy.
6.
Vendor training needs.
An engine monitoring system has been fully installed on Unit 2 and partially installed on Unit 1.
Initial problems are currently being worked out on Unit 2.
When in full operation, it will provide much needed data to help monitor degraded DG operation and help troubleshoot problems more accurately with fewer engine starts.
In addition to the monitoring system, work is progressing on an EPRI sponsored prcject to add artificial intelligence to the DG data collection and evaluation.
Engine Reliability Assessment Considering the seven Valid Failures in the last 100 Valid Tests DG 2A had zero (0) failures in 31 tests and DG 2B had 7 failures in 69 tests.
Two approaches can be used to estimate the reliability. One approach treats each DG as having a separate failure rate. The failure rate for each engine is calculated and the two rates are the multiplied and subtracted from unity to give a system reliability. The second method treats both DGs as having an average failure rate of 7 out of 100 tests (thus each is 93% reliable).
l The estimated failure rate at a 50% cenfidence level (established by NUREG 75/87 Appendix 7-A) is derived using statistical methods assuming a' chi-squared distribution.
Using the first method, DG 2A has a known failure rate of zero (0) which would imply a reliability of 100%. DG 2B has a known failure rate of 0.1014 l=
which corresponds to a reliability of 89.9% (this is very close to the average estimated reliability calculated at the 50% confidence level, 89.3%). The system reliability is thus 100%.
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a s
[
U.S. Nuclocr'R:gulitory Commiccion
' ATTN: Document Control Desk
-June 11, 1990 Attachment No. 2 Page 4 Using the second method, the system reliability is between 99.1% and 99.7%
at a 50% confidence level.
Both methods exceed the 99% goal at a 50% confidence level established by NUREG 75/87 Appendix 7-A.
Basis for Continued Operation i
The unit will continue to be operated because the reliability of the cmergency AC power source exceeds that proposed in the NUREG and a j
comprehensive reliability improvement program is in place, i
Summary of Tests j
The McGuire. Technical Specifications currently require that the DG operability test (PT/2/A/4350/02) be performed once every 31 days if four l
Valid Failures or less have occurred in the last 100 Valid Tests AND if one Volid Failure or less has. occurred in the last 20. Valid Tests. Otherwise, the testing will be performed weekly. The following is a summary of the DG 2A and 2B start attempts.
3 FAIL = VALID FAILURE SUCCESS = VALID SUCCESS INV TEST = INVALID TEST INV TEST FAIL = INVALID TEST FAILURE s
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'U.S. Nuclear.R3gulatory Commission ATTN: Document Control Desk June.11, 1990 Attac}went No. 2 Page 5 INVALID D/G RUN DATE VALTD RESULTS RESULTS 2B 793 05/10/90 FAIL 2B 792 05/10/90 SUCCESS 2B 791 05/03/90 SUCCESS 2B 790 04/26/90 $UCCESS 2A 771 04/23/90 8UCCESS 2B 789 04/19/90 SUCCESS 2B 780 04/12/90 SUCCESS 2B 787 04/12/90 INV TEST 2B 786 04/05/90 SUCCESS 2B 785 03/29/90 SUCCESS 2B 784 03/29/90 SUCCESS 2B
'783 03/27/90 SUCCESS 2A
_770 03/26/90 SUCCESS 2A 769 03/26/90 INV TEST 2B 782 03/22/90 SUCCBSS 2B 781 03/16/90 SUCCESS 2B 780 03/08/90 SUCCESS 2B 779 03/01/90 SUCCESS 2A 768 02/28/90 INV TEST 2A 767 02/27/90 SUCCESS 2A 766 02/27/90 INV-TEST 2A 765 02/27/90 SUCCESS 2B 778 02/22/90 SUCCESS 2B
-777 02/15/90 SUCCESS 2B 776 02/09/90 INV TEST 22 775 02/08/90 SUCCESS 2A 764 02/07/90 SUCC8SS 2B 774-02/01/90 SUCCESS 2A 763 01/30/90 INV TEST 2A
-762 01/30/90 INV TEST 2A 761 01/30/90 INV TEST 2A 760 01/30/90 SUCCESS 2B 773 01/25/90 SUCCESS 2B 772 01/18/90 SUCCESS 2B 771 01/11/90 SUCCESS 2B 770 01/04/90 SUCCESS 2A 759 12/30/09 SUCCESS 2A 758 12/30/89 INV TEST 2A 757 12/29/89 INV TERT 2A 756 12/29/89 SUCCESS 2B 769 12/28/89 SUCCESS 2B 768 12/21/89 SUCCESS 2B 767 12/14/89 SUCCESS 2B 766 12/07/89 SUCCESS 2A 755 12/06/89 SUCCESS
.- ~.
U.S. Nucisar R;guictory Comminaion ATrN Document Control Desk June 11, 1990 Attactment No. 2
.Page 6-INVALID D/G RUN DATE VALID RESULTS RESULTS
?!
2B 765 11/30/89 SUCCESS 2B 764 11/22/89 SUCCESS 2B 763 11/16/89 SUCChSS 2B 762 11/09/89 SUCCESS i
2A 754 11/07/89 SUCCESS 2A 753 11/06/89 SUCCESS 2B 761 11/02/89 SUCCESS 2B 760 10/27/89 SUCCESS 2B 759 10/27/89 FAIL 2B 758 10/19/89 $UCCESS 2B 757 10/12/89 SUCCESS 2B 756 10/07/89 SUCCESS 2B
.755 10/07/89 INV TEST 2B 754 10/07/89 INV TEST 2B 753 10/07/89 INV TEST 2B 752 10/05/89 INV TEST 2B 751 10/05/89. FAIL 2A 752 10/03/89 SUCCESS 2A 751 09/29/89 $UCCESS L
2B 750 09/29/89 INV TEST u
2B 749 09/28/89 SUCCESS l
2B 748 09/28/89 SUCCESS
'2B 747 09/28/89 FAIL 2A 750 09/22/89 SUCCESS 2B 746' 09/22/89 SUCCESS 2A 749 09/18/89 SUCCESS 2A 748 09/15/09 INV TEST 2B 745 09/14/89 SUCCESS 2B 744 09/07/89 SUCCE8S 2B 743 09/05/89 SUCCESS L
2B 742 09/05/89 INV TEST 2B 741 09/05/89 INV TEST 2A 747 09/04/89 INV TEST 2A 746 09/01/89 INV TEST 2A 745 08/31/89-SUCCESS 2B 740 08/31/89 SUCCESS 2B 739 08/31/89 INV TEST 2B 738 08/31/89 INV TEST 2B 737 08/30/89 INV TEST 2B 736 08/30/89 INV TEST 2B 735 08/30/89 INV TEST 2B 734 08/30/89 INV TEST 2B 733 08/30/89 INV TEST 1
2B 732 08/29/89 INV TEST 2B 731 08/29/89 INV TEST
.U.S.-Nuclocr Riguletory Commission i
ATTN: Document Control Desk June 11, 1990
' Attactment No. 2 Page 7 1
INVALIO j
D/G RUN DATE VALID RESULTS RESULTS l
2B 730 08/29/89 FAIL 2B 729 08/29/89 SUCCESS 2A 744 08/24/89 SUCCESS 2A 743 08/24/89 INV TEST 2A 742 08/24/89 INV TEST e
2B 728 08/24/89 INV TEST 2B 727 08/24/89 INV TEST 2A 741 08/23/89 INV' TEST 2A 740 08/23/89 INV TEST 2A 739 08/23/89 INV TEST 2A-738 08/22/89 INV TEST E
2A 737 08/22/89 INV TEST i
12A 736 08/22/89 INV TEST 2A 735' 08/21/89 INV. TEST
,c L
2A 734 08/21/89 INV TEST 2A 733 08/21/89 INV TEST 2A 732.
08/21/89 INV TEST L.
2A 731 08/21/89 INV TEST 2A' 730 08/21/89 INV TEST 2A 729 08/21/89 INV TEST 2A 728 08/21/89 INV TEST L
2A 727-08/19/89 SUCCESS i
i 2A 726 08/18/89 INV TEST FAIL-f 2A 725 08/18/89 INV TEST L
2A~
724.
08/18/89 INV TEST L
2A 723 08/18/89
=INV' TEST 2A 722 08/18/89 INV TEST L
2A 721 08/17/89 INV TEST 2A 720 08/17/89 INV TEST 2A 719 08/17/89 INV TEST 2A 718 08/16/89 SUCCESS 2A 717 08/16/89 SUCCESS 2A
'716 08/15/89 SUCCESS 2A 715 08/15/89 INV TEST 2A 714 08/15/89 SUCCESS 2A 713 08/15/89 SUCCESS 2A 712 08/15/89 INV TEST 2A 711 08/15/89 INV' TEST 2A 710 08/15/89 INV TEST 2A 709 08/15/89 INV TEST 2A 708 08/15/89 INV TEST 2A 707 08/14/89 INV TEST 2A 706 08/14/89 INV TEST 2A 705 08/14/89 INV TEST 2B 726 07/31/89 INV TEST x
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'l U.S. Nuclocr' R2gulatory Consniesion ATIN: Document Control Desk 1
- Jtme 11',1990 Attactuant No. 2 -
i '
Page 8 INVALID D/G RUN DATE VALID RESULTS-RESULTS
-1 25 725 07/30/89 $UCCESS 2B 724 07/30/89 INV TEST 2B 723 07/30/89 INV TEST 2B 722 07/30/89 INV TEST 2B 721 07/30/89 INV TEST 2B 720 07/30/89 INV TEST 2B 719
.07/30/89 INV TEST FAIL L
2B 718 07/29/89 SUCCESS
'2B 717 07/29/89 INV TEST j
l 2B 716 07/29/89 INV TEST L
28 715 07/29/89 INV TEST 2B 714 07/29/89 INV TEST 2B 713 07/27/89 FAIL 2B 712
'07/26/89' FAIL 2:B 711 07/25/89 SUCCESS' 23 710 07/25/89 SUCCESS 23 709 07/25/89 INV TEST 2B 708 07/25/89 INV TEST 2B 707 07/25/89 INV TEST 2B 706
- 07/25/89
.INV TEST 2B 705 07/25/89 INV TEST 2A 704-07/15/89 $UCCESS 2B 704 07/09/89 INV TEST 2B 703
-07/03/89 SUCCESS 2A 703 06/21/89 SUCCESS 2A 702 06/20/89 SUCCESS 2A 701 06/20/89 INV TEST 2B 702 06/06/89 SUCCESS 2A 700 05/19/89 SUCCESS
-2B 701 05/11/89 $UCCESS 2B 700 04/27/89 SUCCESS 2A 699 04/24/89 SUCCESS 2B 699 04/20/89 SUCCESS 2B 698 04/13/89 SUCCESS 2B 697 04/06/89 SUCCESS 2B 696 04/02/89 INV TEST 2B 695 03/30/89 SUCCESS 2A 698 03/29/89 SUCCESS 2A 697 03/28/89 INV TEST FAIL 2A 696 03/28/89 INV TEST 2B 694 03/23/89 SUCCESS 2B 693 03/16/89 $UCCESS 2B 692 03/09/89 SUCCESS 2A 695 03/03/89 INV TEST 2A 694 03/03/89 INV TEST
U.S. Nuclect R:gulatory Commission ATTN Document Control Desk i
- June 11, 1990 Attactumnt No. 2 Page 9-t INVALID D/G RUN DATE VALID RESULTS l
RESULTS 2A 693 03/03/89 INV TEST 2A 692 03/03/89 INV TEST 2B 691 03/02/89 SUCCESS 2A 691 02/24/89 $UCCESS 2B 690 02/23/89 SUCCESS 2B 689 02/17/89 SUCCESS
'2B -
688 02/17/89 INV TEST 25.
687 02/17/89 INV TEST 2B 686 02/17/89 INV TEST 2B 685 02/09/89 SUCCESS 2'B 684 02/02/89 SUCCESS 2A 690 01/30/89 SUCCESS 3
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